Editorial note to: HP Robertson, Relativistic cosmology - Users' Pages

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2108 G. Ellisbasics of horizons were already given by Robertson; their nature was very nicelyclarified by Rindler [45].The huge change since Robertson’s paper has been progress in telescope and detectortechnology, accompanied by developments in computing facilities that can handlethe vast amounts of data generated. This has resulted in the accumulation of detailedobservational data in all wavelength bands for galaxies, radio sources, X-ray sources,and background radiation, as well as gravitational lensing studies of the distribution ofmatter [44,20]. This has refined our estimates of the Hubble constant and the densityof matter in the universe, measured the CBR spectrum and anisotropy pattern over thesky, identified the CBR acoustic peaks and the BAO acoustic oscillations, and confirmedthe presence of both dark matter and dark energy as major dynamical featuresof the recent universe. 15The consensus model—a perturbed RW geometry, with the background dynamicsdescribed by the Friedmann-Lemaître equations (3.2) presented in Robertson’spaper—is now well supported by numerous observations that fit together in a coherentway.The major themes Two of the major unsolved themes of today’s cosmology werealready present in Robertson’s paper: namely the possible existence of dark matter,now regarded as well established, and the possible existence of an effective darkenergy, also now observationally established. Much effort is being expended on tryingto establish the nature of the dark matter, and to determine whether the dark energyis a cosmological constant or something more complex (“quintessence”). Robertsonassumed it was preferred that λ should be non zero, as indicated by present observations.Robertson’s considerations in the paragraph following (10.2) are worth quotinghere. He considers there an R–W model with λ that was initially in a static phasedescribed by the Einstein model, and was knocked out of equilibrium by fluctuationsin density and pressure. He cites a result by Lemaître that the Universe would thenneed 10 10 –10 11 years to attain its present state. Then he says“Such a time scale seems far too short for modern astrophysics, according towhich the ages of the stars... may be of the order of 10 12 years or more.”This comment is important in illustrating how astrophysical and cosmological understandinginfluence each other. This erroneous estimate of the ages of stars was replacedby more realistic ones once the mechanism by which stars emit energy was explainedby Bethe in 1938; together with revised values of the Hubble constant, the age conflictwas then resolved.The basic model described by Robertson—an expanding universe model with a RWgeometry and containing matter, radiation, and a cosmological constant—remains anexcellent model of the universe at recent times, and indeed back to decoupling; butthe present day understanding of times before decoupling is rather different, involving15 The latter assumes the universe is indeed well described by a perturbed RW geometry. An LTB geometrycould in principle do away with the need for dark energy [8,9]; this is one reason why tests of the Copernicanprinciple [41] are important.123
Editorial note to: H. P. Robertson, Relativistic cosmology 2109much more complex physics. The model has had much detail filled in both as regardsits matter content and the superimposed inhomogeneity structure. We have as it weredressed versions of the basic models presented in this excellent early survey paper,written by one of the pioneers of the field.AcknowledgmentsI thank Andrzej Krasiński for helpful comments on previous drafts of this note.Howard Percy Robertson: a brief biographyBy Andrzej Krasiński, compiled and abstracted from Refs. [61] and [62].Howard Percy Robertson was born on 27 January 1903 in Hoquiam, Washington,USA. He was known to his friends and colleagues as Bob. His parents wereGeorge Duncan Robertson and Anna McLeod, Americans of Scottish descent. GeorgeRobertson’s family came from Maryland and he was an engineer who built bridgesin the Washington area. Anna had attended Johns Hopkins and then become a nurse.H.P. was the eldest of his parents’ five children, and when his father died in 1918 hehad to help support the family.H. P. Robertson entered the University of Washington in 1918. He had to earn moneyduring his undergraduate years, so he was unable to participate in the usual studentlife. Originally he began an engineering course, but later he changed to major in puremathematics. He was awarded a bachelor’s degree in 1922 and a master’s degree in1923. Robertson’s studies in mathematics and physics progressed under the influenceof the mathematician E. T. Bell. His relation with Bell was stormy, but deep. It wasBell who urged him to enter graduate work at the California Institute of Technology.Robertson got his doctorate from the California Institute of Technology in 1925after submitting the dissertation “On the Dynamical Space-Time which Contains aConformal Euclidean 3-Space”. His thesis advisor had been Harry Bateman. He wasawarded a National Research Council Fellowship in mathematics to study in Germanywhere he spent the years 1925–1927. Most of that time he spent in Göttingen,but six months of it in Munich. He met Hilbert, Courant, Martin Schwarzschild, vonNeumann, Wigner, Schrödinger, Heisenberg and Einstein. He impressed Courant andHilbert with his mathematical skills, and, in addition to that, left an amusing mark of arather exceptional type: “... he rolled a barrel of beer through cobbled Munich streetsat 2:00 A.M. and thus earned a police citation for ‘disturbing the citizenry’ ” [62].He returned to the California Institute of Technology in 1927, where he wasappointed assistant professor of mathematics. Two years later he was appointed assistantprofessor at Princeton, where he worked for 18 years, later as associate professorand then full professor, in both the mathematics department and the physics department.A second course of his career began in 1939 when World War II started. Althoughthe United States was initially not involved in the war, Robertson became, under theurging of Richard Tolman, a member of a group which was to become part of theNational Defense Research Committee. They studied the effectiveness of explosivesand the mathematical theory of explosion damage. After the fall of France in May1940, Robertson was given the position of liaison scientist with Britain. Over the next123
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